Since Gallup started asking Americans in 1969 whether use of marijuana should be legal, most have said no. But in a Gallup poll released yesterday, half of Americans said the government should legalize pot use.

That is a record high.

Here's Gallup's historical chart for the question:

And here's how they characterize the shift in public opinion:

When Gallup first asked about legalizing marijuana, in 1969, 12% of Americans favored it, while 84% were opposed. Support remained in the mid-20s in Gallup measures from the late 1970s to the mid-1990s, but has crept up since, passing 30% in 2000 and 40% in 2009 before reaching the 50% level in this year's Oct. 6-9 annual Crime survey.

...

If this current trend on legalizing marijuana continues, pressure may build to bring the nation's laws into compliance with the people's wishes.

The why of the rise in support seems hard to pin down. Gallup hints that it has something to do with marijuana's popularity. Citing the National Organization for the Reform of Marijuana Laws, it says pot is the "third-most-popular recreational drug in America, behind only alcohol and tobacco."

The findings come less than six months after the federal government ruled that marijuana should remain classified as a Schedule 1 drug, which means the government considers it as dangerous as heroin.

In June, Michele M. Leonhart, head of the U.S. Drug Enforcement Administration, said that marijuana would remain classified as Schedule 1 because it "has a high potential for abuse" and "has no currently accepted medical use in treatment in the United States."